1. Field of the Invention
The present invention relates to high power lasers and amplifiers, and more specifically, it relates to alkali vapor lasers and amplifiers pumped with at least one laser diode that has a spectral width of at least 0.01 nm.
2. Description of Related Art
The largest market currently for high-power (>kilowatt) lasers is for the materials processing applications of sheet-metal cutting and welding.
Application end-users continue to call for multi-kilowatt lasers with improved output beam quality, wavelengths that are <1060 nm, higher efficiency and compactness, and decreased cost-of-ownership, compared to traditional lamp-pumped Nd:YAG solid state lasers and electrically-pumped CO2 gas lasers.
The near-diffraction-limited (i.e., M2<2 or 3, where M2 is the times-diffraction-limit factor) feature provides for greater intensity on the work-piece, for a focusing lens having a given f/number. Shorter wavelengths in general result in enhanced absorption efficiency in most metals and allow for power delivery to the work piece by optical fiber. Higher efficiency and compactness generally lead to low cost of ownership.
The direct use of high-power 2-D laser diode arrays for material processing applications has been of great interest in the past few years. However, the output beam of a high-power (60 watt) linear bar array of laser diodes is typically >1000 times the diffraction limit, and that of a 2-D stack of bar array is typically more than several thousand times the diffraction limit. Efforts continue to improve beam quality of 1-D and 2-D laser diode arrays, but cost effective methods appear to be complex and expensive.
An alternative means of effectively improving the beam quality and/or spectral width of highly multi-mode 1-D and 2-D laser diode arrays is to use them to pump another laser, whose output beam can be extracted in a low order spatial mode (e.g., near-diffraction-limited, or M2=2 or 3), and/or with a greatly reduced spectral width. In effect the pumped laser becomes a “spatial and/or spectral brightness converter”, trading a small loss in energy efficiency for a much greater gain in beam quality and/or spectral narrowness. The diode-pumped solid-state laser (DPSSL) is such a brightness converter. Nd:YAG DPSSLs have been developed recently that exhibit increased efficiency and beam quality compared to traditional lamp pumped devices.
Notwithstanding the reduced (˜⅓) thermal loading realized by diode pumping (compared to lamp pumping), practical, near-diffraction-limited, multi-kilowatt Nd:YAG DPSSLs have remained elusive because of severe thermally induced focusing and stress-birefringence present in solid state laser hosts, such as YAG.
In light of the foregoing, the need continues for a cost-effective solution for an efficient, compact, multi-kilowatt, laser source emitting at a wavelength <1060 nm, and with a near diffraction-limited and/or narrow-spectral-band output beam.